Equipping wind turbine rotor blades with one or more electrical heating elements in order to be able to heat surface regions of the rotor blade is known. In this way, it is possible to counteract icing of the rotor blade, either in that ice accumulation is entirely prevented or ice already adhering to the blade surface is melted. Known electrical heating elements are usually arranged in the region of the profile leading edge and, along a majority of the rotor blade length, on the surface thereof. During operation, they are supplied with an electrical heating current which flows through the heating element for example in the longitudinal or transverse direction. The desired heating action is brought about by the ohmic resistance of the heating element.
For optimal operation of the heating element, uniform heat generation is desired over the entire surface area thereof. This requires an electrical resistance that is uniform over the surface area of the heating element or is adapted to the locally required heat output. Deviations arise in particular in the region of defects of the heating element. These can be brought about by production errors, transportation damage or by mechanical damage during operation of the wind turbine rotor blade. Lightning striking the wind turbine rotor blade in the region of the heating element, or flashovers between the heating element and a lightning conductor can likewise cause defects.
In the region of a defect, the electrical conductivity of the heating element is impaired or entirely interrupted. This results in two undesired effects: in regions of the heating element which are laterally adjacent to the defect with regard to the heating current direction, a greater current density and consequently higher temperatures occur. These regions are also known as hotspots. Moreover, within the defect and upstream or downstream of the latter in the heating current direction, regions with an insufficient temperature occur. These regions are also known as cold spots. Both effects can result in undesired damage. In particular in the region of extensive cold spots, the heating element can under certain circumstances no longer prevent ice accumulation. In the region of the hotspots, it is possible for temperatures which are so high to arise that the laminate, in particular a plastics matrix surrounding the reinforcement fibers, is damaged, and so structural, and under certain circumstances irreparable, damage to the wind turbine rotor blade can occur in the worst-case scenario.
In a known method for repairing electrical heating elements, an attempt is made to restore the original electrical conductivity of the heating element in the region of the defect. To this end, an electrically conductive material, preferably the same material as the one of which the electrical heating element is made, is applied to the heating element in the region of the defect and preferably brought into electrical contact with the heating element in the region of its edges. The establishment of an electrical contact between the heating element and the repair patch requires complicated mechanical preparation of the contact points, this frequently not being feasible at the site of a wind turbine. Independently thereof, it is difficult to restore the original resistance ratios of the heating element. In particular at the electrical contact points, it is possible for regions with a high current density, which can themselves result in hotspots, to occur.